#include <stdio.h>
int main() {
    int a, b, c, d;
    float x, y;
    scanf_s("%d %d %d %d", &a, &b, &c, &d);
    x = (float)a / b;
    y = (float)c / d;
    printf("%.4f\n", x+y);
return 0;
}